1. Field of the invention
The present invention generally relates to an ink jet recording apparatus and an ink jet recording method.
2. Description of the Related Art
There has been a color ink jet recording technique for recording images by discharging liquid ink droplets from nozzles. Having a simple structure and reduced printing noise, this color ink jet recording technique is suitable for small-sized printers. To obtain a high-quality image without ink bleeding, however, it is necessary to use special paper sheets such as coated paper sheets each having an ink absorbing layer formed thereon. On plain paper such as copy paper, ink bleeding is easily caused in each boundary area between different colors.
To counter this problem, there has been a method for reducing ink bleeding between colors by increasing the permeability of ink with paper sheets. With this method, however, there is a problem of poor sharpness (feathering) along the edges of lines and characters printed especially with black ink.
To increase the image quality of lines and characters, there has been a technique for reducing bleeding between color inks by employing the color inks each having a higher permeability than the black ink with a low permeability. By this technique, however, ink bleeding cannot be prevented between a black ink printed region and a color ink printed region that are adjacent to each other and have different permeating rates. Conventional techniques suggested to counter this problem are as follows.
Japanese Patent Application Publication No. 6-113155 (Patent Document 1) discloses a device that converts print pixels in each boundary area between black ink regions and color ink regions in an image so as to prevent bleeding between the black ink and the color ink.
Japanese Patent Application Publication No. 10-067125 (Patent Document 2) discloses a device that sets a time interval between black ink application and color ink application onto a recording paper sheet so as to prevent ink bleeding. Japanese Patent Application Publication No. 11-077992 (Patent Document 3) discloses a device that measures the recording density based on image data, and, according to the recording density, switches recording modes for each main scan.
In a case where black ink having a low permeating rate is employed to increase the print quality with the black ink, ink transfer between printed paper sheets in a high-speed printing operation is caused due to the low fixing speed. To counter this problem, there has been a technique (Prior Art 4) of applying color ink having a higher permeability before applying black ink and utilizing a chemical reaction between black ink and color ink so as to increase the ink fixing speed.
With the device disclosed in Patent Document 1, however, excessive pixel conversion to prevent ink bleeding leads to the appearance of white lines on the boundaries between black pixels and color pixels, as the color pixels that are adjacent to the black pixels are converted into blank data. If the black pixels that are adjacent to color pixels are converted into color data, the image quality in the black image region deteriorates, as the brightness in the converted region becomes higher than the brightness of the black ink and the higher brightness results in an insufficient density. In this manner, if a very large number of pixels are converted to prevent ink bleeding, image deterioration is caused for a different reason.
With the device disclosed in Patent Document 2, there is a problem in that the actual printing speed greatly decreases, though ink bleeding can be prevented by setting a certain time interval between the black ink application and the color ink application.
With the device disclosed in Patent Document 3, there is a problem in that the recording modes are switched even for image data that cause little ink bleeding, resulting in an unnecessary decrease in printing speed.
In Prior Art 4, the color ink needs to be applied onto the paper sheet before the black ink. Therefore, printing is performed by separate scans for applying the black ink and the color ink, also resulting in a decrease in printing speed.